There is high prevalence of unhealthful diet and physical activity patterns in adolescents. Ecological models posit that health behaviors are influenced by individual, social/cultural, policy, and environmental variables. Data on all levels of influences are needed to guide multi-level interventions, but most studies have been limited to individual and social/cultural variables. Studies of adults have demonstrated consistent associations of community design ("walkability") and recreational environments with physical activity, and a few studies suggest neighborhood food environment is related to eating patterns. Such data in young people are limited. The present study aims to evaluate the ability of a multi-level model to explain variation in physical activity, sedentary behavior, dietary patterns (energy, fat and fruit and vegetable intake) and weight status in adolescents, with an emphasis on neighborhood environments. Neighborhoods in two regions in the U.S. (Seattle-King County, WA and Baltimore-Washington, DC) will be selected for study. 48 neighborhoods (n=24 per region) will meet criteria for cells in a 2 X 2 matrix defined by high vs low walkability (combination of street connectivity, residential density, land use mix, and retail floor area ratio) and high vs low median income. Eighteen adolescents aged 12 to 16 and a parent will be randomly selected from each neighborhood (n=864 total). Walkability indices will be created through existing parcel-level and street network databases. Pedestrian infrastructure, public recreation space, and nutrition environment quality indices will be created through psychometrically sound direct observation instruments. Additional correlates will include crime and weather;psychosocial variables assessed by instruments specific to each target behavior;parent support;neighborhood preference: and perceived neighborhood, school, and home environments. Physical activity will be measured with 7 days of accelerometer monitoring;diet by 3 random 24-hour recall interviews;sedentary behaviors by self-report, and height and weight by adolescent and parent reports. Behaviors will be re-assessed 6 months later to investigate seasonal effects. Substantial measurement development has been completed, and the team has published several papers on innovative measures. The transdisciplinary project team has experience in all components of the study and a strong record of collaboration. Building on funded studies in the same regions creates substantial cost savings. The proposed study is based on a specific ecological model, emphasizes objective measurement, targets an at-risk, under-studied age group, and has the potential to inform intervention approaches that could produce population-wide improvements in multiple health behaviors and contribute to reducing the obesity epidemic.